Thursday, June 18, 2009

First Light IV

This is the 4th installment of a thread concerning the construction of a Japanese post-mounted garden lantern - - my interpretation of the form at least. In the the previous postings, I detailed the construction of the support post, and the first 'X' assembly of the lower support arms, hijiki.

Today I'll show some pictures of the making of the secondary 'X' in the lower support arm group. To lap joint four pieces of wood together in one plane would have meant, in the case of, say. a 2" tall piece of wood, that each lap would have 1/4 of the available wood, or 0.5". This means that each piece, having 75% of it's meat cut away, would be rather weak. Now, in a shōji door/window, where in certain patterns there might be many such 4-way interconnections between lattice bars, kumiko, and the loading on the bars primarily that of gravity and working to the 'strength' of the four pieces at the lap (i.e., not against the stress risers present at the inside corners of the lap notches), the four way lap is a possible solution. As often as not, mind you, the strategy in shōji with this form of lattice pattern is actually to lap two pieces and fit the other intersecting kumiko in place strictly by compression. That's not an option in the case of this particular lantern's support arm joinery however.

In the case of the double 'X' of these lower support arms on the lantern, where the loading works against the strength of the lap, and in fact even cantilevers the load directly into the lap, I thought it would be better to not go with a 4-way lap. My idea is to lap the two pieces that are normal to the post faces, 50% each, so they keep a fair amount of their strength, and to attach the diagonally-oriented hijiki with a housed joint. This joint would give some resistance to the cantilevering loads, but more than that it is simply serving to lock the diagonal hijiki to the main two cross-lapped pieces such that they can't withdraw. Also, I will make up for this loss of strength in the diagonal hijiki on the lower level, by reconfiguring them in the next layer of double 'X' braces.

First, I cut the housings on the lower pair of hijiki:

When assembled, the cross lap forms a housing which will trap the nose of the diagonal support arms:


Then I started cutting the nose of each diagonal arm; a one..:


...and 'a two':


Then a little paring to clean the surface up:


One the four diagonals were cut, I marked them for location, then slid them into place and made any necessary small adjustments to the fit so as to get a clean abutment, best I can:


After the fit was acceptable, I could start marking out the cut lines for the male part of the joint:


This is the topside:


And the underside:


Time for the next installment of that international hit tv show, Sawing for Teens:


The 'Sawing for Teens' reference is to a scene from an Canada National Film Board animated short from a bout 20 years ago called The Big Snit, in which a couple of argumentative people are playing Scrabble at home, oblivious to an unfolding nuclear war.... (trust me, it was pretty funny!)

Anyhow, after the butchery with the handsaw was complete, the end of the tenon looked like this:


A bit of paring to clean it up and then we have this:


I then acquainted the diagonals with their cozy new home:


Lastly, I tapped the main 'X' brace back into place, thus trapping the diagonals and holding them firm. At this stage the length of the diagonal support arms has been left a bit long as you can see. Reason: it's easier to work with longer pieces than short and it gives me room to make small corrections with layout for the next layer of parts if there is some slight misalignment with any of them:


It seems to work. It also 'works' that my lovely wife is out of town for a week, so I can make a mess of the kitchen, my palatial new shop space, without fear of strangulation.

In the next installment I'll chop the support arms in half by accident (hopefully not!) and configure them into their final shape, which is in the 'boat shape bracket arm' form, or funa hijiki (舟肘木).

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